Paper stock material such as the material for paper towels and toilet tissue is manufactured as a wide continuous web that is wound onto very large parent rolls. Subsequently, in a rewinding machine, each such parent roll is unwound and is simultaneously rewound onto tubular cores to form numerous individual rolls. The rewinding operation usually involves a simultaneous lengthwise slitting of the web as it is unwound from the parent roll, to reduce it to the widths desired for the individual rolls. During the rewinding operation the web may also be embossed, and it may be perforated across its width, at regular intervals along its length, to define readily detachable rectangles in the individual rolls.
The rewinding operation should obviously take place at the highest possible speed, and it is also necessary that each individual roll should be wound both to a specified diameter and with a specified count or footage. The problem of meeting both diameter and footage or count requirements is particularly severe in the rewinding of so-called hard wound rolls of paper towels and the like that are intended for industrial and commercial use, where the objective is to produce an individual roll small enough to fit into a cabinet or dispenser of a given size but having a specified high count or footage. To produce such hard-wound rolls, the web must be under some tension during rewinding, and the need for maintaining such tension tends to complicate certain problems that are always presented by high-speed automatic web rewinding machines.
In an automatic rewinding machine, a tubular core is loaded onto a winding mandrel before the winding operation begins, to provide cores onto which individual rolls are to be wound. The winding machine usually comprises a rotatable turret by which several mandrels are carried for orbital motion through successive stations at which mandrel loading, core preparation, winding, and mandrel unloading are performed.
After the core has been loaded onto a mandrel, it is cut into shorter individual core lengths, and at about the same time an adhesive coating is applied to the core. The mandrel and core are then brought up to a rotational speed such that the peripheral speed of the core substantially matches the linear speed of the web. As the winding of one roll is finished, the web must be cut through to separate it from the finished roll, and the leading end portion of the web that results from this cutting operation must be attached to a new core.
Cutting of the web and transfer of the winding operation from a completed roll to a new core must take place during a very brief and critical interval. The speed at which cutting and transfer can be successfully accomplished essentially determines the rate at which the entire rewinding procedure can take place, because it is not practicable to slow down the web during the critical interval inasmuch as the parent roll from which it is unwound is too massive to be subjected to substantial short term accelerations and decelerations.
In early automatic rewinding machines, as exemplified by U.S. Pat. No. 2,769,600 to Kwitek et al, the web was cut through at a location between a fully-wound individual roll that was moving out of the winding station and a new core that was moving into the winding station. Such web severing was effected by means of a radially extensible and retractable knife blade that was carried by a large diameter bed roll around which the web had a partial wrap. When extended from the bed roll, the knife blade cooperated with other extensible means on the bed roll for engaging the web against the new core. The knife blade had to be in its retracted position as it passed the new core and had to be fully extended immediately after it passed the new core and before it was carried orbitally past the fully wound core, which is to say that the knife blade had to move from its fully retracted position to its fully extended position within a relatively small fraction of a turn of the bed roll. Sufficiently rapid movement of the knife blade was feasible if the bed roll was rotating rather slowly. But with web speeds on the order of thousands of feet per minute, and correspondingly high rotational speeds of the bed roll, it became difficult to achieve the necessary synchronization of knife movements with bed roll rotation, and the rapid movements of the knife relative to the bed roll imposed high stresses upon the machine.
U.S. Pat. No. 2,585,226 to Christman disclosed web winding mechanism wherein the web was cut through at a location ahead of the new core and was carried to engagement with the new core by a feed roll to which the leading portion of the web was caused to adhere by suction. Suction adhesion, while satisfactory in low-speed operations, does not lend itself to operation at extremely high speeds of feed roll rotation because suction cannot be applied and relieved in the very small fractions of a second that are involved in web severing and transfer. Furthermore, the expedient taught by the Christman patent does not seem to be suitable for hard roll winding because it is doubtful whether web tension could be maintained during an interval in which the web was held to a feed roll only by suction.
The later U.S. Patent to Nystrand et al, U.S. Pat. No. 3,179,348, reissued as U.S. Pat. No. Re. 28,353, disclosed another type of apparatus in which the web was cut through before it was brought into contact with the new core and wherein its free leading portion that resulted from the cut was carried through a fraction of a revolution by the bed roll, which engaged it against the new core. Although the apparatus of Nystrand et al would seem to be better adapted for highspeed hard roll winding than that of Christman, it was apparently not satisfactory for that purpose in actual practice.
In the apparatus of the Nystrand et al patent, the web ran in partially wrapped engagement with a driven bed roll that had a longitudinally extending recess in its surface and had parallel blade elements that were extensible out of the recess to engage the web for making the cut therethrough. Cutting was done by a knife blade that was fixed on a chopper roll rotating adjacent to the bed roll, which knife blade was received between the parallel blade elements on the bed roll. The cut was made through a part of the web that had not yet arrived at the new core. In order to maintain control over the free leading portion of the web that resulted from the cut through it, the bed roll carried a set of sharp pins that were radially extended from it along with the parallel blade elements, and these pins, in cooperation with a resilient pad on the chopper roll surface, impaled the leading portion of the web to connect it to the bed roll.
After such impalement, the blade elements and the pins began to retract so that they could clear the new core that they were now approaching, and a set of finger-like pressure pads then extended radially from the bed roll to disengage the web from the pins and press the web into engagement with the new core.
The blade elements and the pins were carried by one assembly that extended and retracted relative to the bed roll, and the pressure pads were carried by another such assembly. Each of these assemblies was eccentrically carried on a shaft that rotated through a partial turn in each direction for the respective extending and retracting motions. To avoid interference between the pin and blade element assembly and the pressure pad assembly, the shaft for the pressure pad assembly had to be located circumferentially behind those pads relative to the direction of bed roll rotation. Owing to this rearward location of the axis about which the pressure pads made their pivoting extension, that portion of the surface of each pressure pad that was effective to press the web against the new core had to be curved on a relatively small radius; and this meant that there were only a very few degrees of bed roll rotation in which the transfer pads could be effective to engage the web firmly against a new core. However, the point in bed roll rotation at which the web became disengaged from the pins was somewhat indefinite, because the curvature of the web engaging surfaces of the pressure pads did not make for a positive detachment of the web from the pins, and the rearward component of extending motion of the pressure pads carried them away from the pins and thus decreased their effectiveness for web release. To further diminish the possibility of effecting release of the web from the pins at a well defined point in bed roll rotation, Nystrand et al expressly recommended that the pressure pads extend "relatively slowly". Under all of these circumstances there could be no assurance that the web would be firmly engaged against the new core substantially simultaneously with its disengagement from the pins.
If the web was not under tension--and it was not meant to be with the Nystrand et al apparatus--small errors in the timing of transfer of the web from the pins to the new core were of no practical consequence. But with a lengthwise tensioned web, there can be no delay between release of the web from its impalement on the pins and its engagement against the new core, and such engagement must be firm and positive. The type of action of the pressure pads that is needed for winding with a tensioned web can be assured only if the pins and the pressure pads are so arranged that pressure pad extension does not have to be timed to within very small limits of bed roll rotation. Such extremely accurate timing would have been necessary in order to use the Nystrand et al apparatus for tensioned web winding, but would have been practically unattainable with it, owing to the arrangement of its mechanism.
Another feature of the Nystrand et al arrangement that made it particularly unsuitable for the winding of a tensioned web was that the parallel blade elements and the pins moved radially outwardly against the web and thus had to force the web away from the bed roll and into engagement with the knife blade on the chopper roll. With an untensioned web no great force was needed to effect this extending motion and web displacement, but with a tensioned web very high forces would have had to be applied to the assembly comprising the blade elements and pins in order to drive it out against web tension.
Those skilled in the art apparently did not appreciate that the above explained deficiencies made the Nystrand et al apparatus unsuitable for tensioned web winding. It clearly was not obvious to them how to overcome those deficiencies.
There is no suggestion in any of the above discussed prior patents concerning another and very important problem that is posed by the need for maintaining tension upon a web during hard roll rewinding: the torque applied to the web winding mandrel must be controlled for maintenance of web tension. In prior automatic rewinding machines the winding mandrel was driven in such a manner that web tension tended to control rotational speed of the winding mandrel, and there was no attempt to control applied torque. As can be seen from the above mentioned patents, the usual prior arrangement was to mount a number of core-carrying mandrels for free rotation on the turret by which the mandrels were carried from station to station in orbital motion. Each mandrel had its own coaxial drive sheave. As a mandrel was carried towards the winding station, its drive sheave came into engagement with a stretch of a drive belt that was running at a constant speed. Engagement of the sheave against the drive belt served as a clutch connection by which the mandrel was brought up to winding speed and which tended to rotate the mandrel at a constant speed as long as the drive sheave remained in engagement with the belt. Since the sheave could slip relative to the drive belt--and was intended to do so--there could be no really accurate control of the torque applied to the mandrel, and consequently there was no possibility of maintaining the web tension needed for hard roll winding.
The problem of providing a mandrel drive system for hard roll winding is complicated by the fact that a high speed automatic web rewinder must comprise several mandrels. During a time when web tensioning torque is being applied to a mandrel at a winding station, to drive it for web winding, a mandrel at a proceding station must be accelerated from a stop, to bring the peripheral speed of a core thereon into substantial match with the existing speed of web advance. At that same time, still another mandrel, carrying a completely wound roll, is being decelerated to a stop in preparation for unloading; and meanwhile other mandrels must remain stationary. The problem, of course, is to provide the requisite modes of drive for the respective mandrels at the proper times, and to do so without interfering with indexing rotation of the turret or requiring costly or unwieldy drive means.
When the web is first transferred to a new core, it is secured to the core by adhesive that cannot support a high web tension, and the mandrel has to make several turns before the web has sufficient wrap around the core to allow tension to be applied to the web from the core. In practical effect this means that web tension must in some manner be relaxed during the first few turns of winding onto a new core, and must thereafter be picked up and maintained by means of the torque applied to the core. Such controlled change in web tension should of course be accomplished in a simple manner.
Another problem that relates to the driving of mandrels for hard roll rewinding is an economic one. Heretofore it has been thought that high power was needed for driving the winding mandrel, so that a high torque could be applied to it for maintenance of the necessary web tension. On this premise, stringent footage and diameter specifications now being laid down for hard-wound rolls would require use of very large motors for mandrel driving. Such motors, in addition to being expensive in themselves, would have a high energy consumption, and production of very compact hard-wound rolls would become undesirably expensive. Furthermore, with a powerful motor driving the winding mandrel, the high torque imposed upon the mandrel would have to be transmitted to the web through the core, and an adequately slipless connection between the mandrel and the core could result in deformation of the latter.
Maintaining a required count or footage on each individual roll is a problem that is encountered with the winding of an untensioned web but is probably more severe with hard roll winding because of the need for also maintaining a closely specified diameter for the roll. Hence it is especially desirable to provide for quick and easy minor adjustments to the count or footage when hard-wound rolls are being produced. With prior automatic web rewinding apparatus, adjustability of the count was difficult and expensive because all phases of the cycle of loading of cores, core preparation, winding, and unloading were interdependent and were timed in relation to one another and to the rotation of the bed roll by a system of gears, sprockets or the like. Any change in the count required an expensive and time consuming change in the synchronizing gear system. Obviously, if it is found desirable to make a one-turn increase in the number of bed roll rotations for a finished individual roll--for example, to compensate for unusually "stretchy" web stock--it is undesirable to effect such change at the cost of providing the machine with a whole new gear system.